Conventional wisdom in the art holds that it is advisable to use a relatively shallow web taper rate in twist drills so that the flute depth along the length of the flute is as great as practicable. This should provide the maximum amount of volume to convey chips, swarf or sawdust back from the tip and out of the hole being drilled. This convention is embodied in two Standards: The American Society of Mechanical Engineers (ASME B94.11M-1993), and The National Aerospace Standard of the Aerospace Industries Association of America, Inc., (NAS 907) (hereinafter collectively referred to as "Standards"), both of which Standards are specifically incorporated in their entireties by reference herein. The Assignee of the present invention has been selling conventional Jobber-length, straight-shank drill bits which have parameters that track the Standards, and which have conventional web thickness taper rates between 0.024 inches to 0.030 inches. Also, it has been selling a self-centering drill bit with pilot tip under the BULLET.RTM. trademark having a web taper rate of about 0.027 inches per inch of flute length. This self-centering drill bit was designed with the end user who uses a portable drill in mind, particularly one who desires a bit which is optimized to drill in both metal and wood. The first versions of these bits are disclosed in U.S. Pat. Nos. 4,968,193, issued Nov. 6, 1990, to Chaconas et al., and 5,288,183, issued Feb. 22, 1994, to Chaconas et al., each of which is assigned to the same Assignee of the present invention. The entire disclosures of each of these two patents are also specifically incorporated by reference herein.
One of the needs of an operator who uses the bit in a hand-held power drill is increased toughness, or resistance to breaking (typically in the flute portion of the drill bit). The increased robustness is needed because in metal drilling the portable power drill user puts considerable side stresses on the drill bit, not having the stability that a drill press provides. However, the BULLET.RTM. drill bit, which was optimized to drill well both in metal and in wood, not only needs strength while drilling metal, it also must drill holes through wood with a minimum of "woodpeckering", that is, repetitively retracting and reinserting the drill bit to clear the flutes of sawdust. There is also a need to enhance the BULLET.RTM. drill bit's longevity if it should be subjected to an overspeed condition in metal, as well as the strength in its tip portion. Finally, there is a need to reduce its tendency to produce a disc in laminated materials.